N=int(input())
K=int(input())
def f(p,d):
	L=len(p)
	q=[0]*(L+5)
	for i in range(L):
		n=p[i]
		if n:
			for j in range(6):
				q[i+j]+=d[j]*n
	return q
d=[1]*6
k=[0]*3+[2]*3
p=[1]
q=[1]
for i in range(N):
	p=f(p,d)
	q=f(q,[d,k][i<K])
L=len(p)
u=[0]*L
w=[0]*L
for i in range(1,L):
	u[i]=u[i-1]+p[i-1]
	w[i]=u[i]*q[i]
print(sum(w)/36**N)